Lift apparatus

ABSTRACT

When a plurality of hydraulic cylinders are actuated for lifting or lowering a platform, the platform and the load applied to it are supported by a plurality of locking plates coupled to the cylinders and each having a plurality of trapezoidal teeth in engagement with the similar teeth of a rack attached to a post along which the platform is lifted or lowered. Lever means are provided for locking in position the platform for a long time even when the hydraulic pressure is not applied to the locking cylinders which cause said locking plates to engage with the racks.

ihlited States Patent 1 Itoh et al.

[54] LIFT APPARATUS [75] Inventors: lsamu Itoh, Koenji-Minami, Tokyo; Fumio Nakazono, Funabashi, both ofJapan [73] Assignee: lshikawajima-Harima Jukogyo Kabushiki Kaisha, Tokyo-to, Japan [22] Filed: Dec. 22, 1971 [21] Appl. No.: 210,924

[52] US. Cl ..254/105 [51] Int. Cl. .;B66f 1/00, E02 d 21/00 [58] Field of Search ..254/105l08 [56] References Cited UNITED STATES PATENTS 2,963,868 12/1960 Armstrong ..254/l05X 51 Mar. 27, 1973 Grant et al ..254/l05 X Johnson ..254/l07 X l/l96l 4/1969 Primary Examiner-Othell M. Simpson Attorney-Samuel Scrivener, Jr. et al.

[57] ABSTRACT are provided for locking in position the platform for a long time even when the hydraulic pressure is not applied to the locking cylinders which cause said locking plates to engage with the racks.

2 Claims, 2 Drawing Figures LIFT APPARATUS The present invention relates to generally an elevating machine and more particularly a lift apparatus for lifting or lowering a working platform along a post or the like.

In general, the prior art lift apparatus of the type described may be divided into two types. In one type, a pinion and rack system is employed tolift orlower a working platform, whereas in the other type, hydraulic cylinders are employed for lifting or lowering the platform.

In the conventional lift apparatus utilizing the hydraulic cylinders, the working platform is locked in a desired height by placing a pin or plate between the post and the lift device or devices. Itis difficult to insert the pin or plate or remove it, and, furthermore, the

force from the hydraulic cylinders is transmitted through a box to the locking pin or plate so that the strength of the box must be increased. Furthermore the platform is generally lifted or lowered only intermittently.

The present invention was made to overcome the various problems encountered in the prior art lift apparatus utilizing the hydraulic cylinders. One of the objects of the present invention is to provide alift apparatus capable of lifting or lowering a platform continuously by a double-action mechanism comprising at least two pairs of hydraulic cylinders.

Briefly stated, a lift apparatus in accordance with the present invention is characterized by comprising a post, a platform fitted over said post for slidable vertical movement, a plurality of racks each of which has trapezoidal teeth and a pair of guides extended on both sides thereof in the longitudinal direction thereof, and which is attached to the outer surface of said post in the axial direction thereof; a plurality of lift devices disposed below said platform for lifting or lowering said platform, each of said plurality of lift devices comprising a box formed with a pair of guide shoes .slidably fitted over said guides respectively, a locking plate which has a plurality of trapezoidalteeth adapted for engagement with said trapezoidal teeth of said rack and which is slidably fitted into said box', a pair of lock cylinders operatively coupled to said box and said locking plate so as to cause said locking plate to engage with or disengage from said rack, and a plurality of lift cylinders operatively coupled to said platform and to said locking plate in said box; and a plurality of locking devices disposed above said platform for supporting and locking in position said platform, each of said plurality of locking devices comprising a boxvformed with a pair of guide shoes slidably fitted over said guides of said rack respectively, a locking plate which'has a plurality of trapezoidal teeth adapted for engagement with said trapezoidal teeth of said rack and which is slidably fitted into said box, a pair of locking cylinders operatively coupled to said box and said locking plate so as to cause said locking plate to engage with or disengage from said rack, and a rocking lever interconnecting said lock plate in said box with the top surface of said platform.

The advantages of the lift apparatus of the present invention may be summarized as follows:

i. The platform may be continuously lifted or lowered at high speed because of the double-action mechanism;

ii. The platform can be securely locked in position for a long time by the mechanical locking means (even when no hydraulic pressure is applied to the locking cylinders);

iii. Each of the upper boxes of the locking devices is connected to the platform with a rocking lever which constitutes a locking mechanism, so that the force such as reversing moment will not exert directly to the racks on the post and the upper boxes, whereby the breakdown can be prevented;

iv. The trapezoidal teeth of the locking plate may easily engage with those of the rack, and since at least two teeth are provided, the load exerted to the locking plate may be uniformly shared by the two teeth and even if one of them should be broken, the engagement of the locking plate with the rack can be ensured by the remaining tooth;

v. Because of the trapezoidal teeth, the engagement of the locking plate with and the disengagement thereof from the rack may be rnuchfacilitated; and

vi. Since the force from the hydraulic cylinder may be directly exerted to the locking plate, the force transmission may be improved as compared with the type in which the force is transmitted through the box.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiment thereof taken in conjunction with the accompanying drawing.

FIG. 1 is a side view of a lift apparatus in accordance with the present invention looking in the direction indicated by the arrow A in FIG. 2; and

FIGS. 2-8, -C, -D and -E are views looking in the directions indicated by' the arrows B, C, D and E in FIG. 1.

A cylindrical vertical post or column 1 extends through a platform 26, and a plurality of plates 22 (only four are shown in the drawing) are securely fixed to the outer surface of the cylindrical column 1 in equiangularly spaced apart relation. A rack 2 having trapezoidal teeth and a pair of guides 3 attached to both sides of the rack 2 is securely attached to each of the plates 22 by for example welding.

Four lower lift devices or mechanisms attached to the racks 2 below the platform 26 are all similar in construction, so that it will suffice to explain one lower lift mechanism. Each lower lift mechanism comprises a pair of upper and lower guide shoes 10 and 10' slidably fitted over the guides 3 respectively, a pair of plates 11 each of which has an elongated slot 25 and connects the pair of upper and lower guide shoes 10 and 10' to form a lower box 23, a pair of lock cylinders 5 whose inner ends are pivoted to the lower box 23, a lock plate 6 which has trapezoidal teeth 2 adapted to engage with the teeth of the rack 2 and to which are pivoted the rods or plungers of the lock cylinders 5 so that the lock plate 6 may be slidable between the pair of plates llto engage with or disengage from the teeth of the rack 2, and a pair of lift cylinders 4 whose upper ends are pivoted to a clevis 9 fixed to the undersurface of the platform 26 with a pin 8 and whose rods or plungers are connected to the lower boxes 23 with a pin 7 extending through the elongated slots 25 of the plates 11 and the lock plate 6.

Two pairs of these lift mechanisms are alternately actuated to lift continuously the platform 26. More specifically when the rods or plungers of the lift cylinders 4 of the first pair of lift mechanisms which are angularly spaced from each other by 180 (right and left lift mechanisms in FIG. 1) are extended, the rods or plungers of the lift cylinders of the other pair of lift mechanisms (one being shown at the center in FIG. 1) are extracted as will be described in more detail hereinafter.

Above the platform 26 are disposed four platform supporting-and-locking devices similar in construction to the lower lift mechanisms or boxes 23. Each of these devices comprises a pair of guide shoes 17 and 17' slidably fitted over the guides 3 of the rack 2, a pair of plates 18 each having an elongated slot 25 and connecting the pair of upper and lower guide shoes 17 and 17' to form an upper box 24, a lock plate 16 which has trapezoidal teeth 2' adapted to engage with the teeth of the rack 2 and which is slidably fitted into the box 24, a pair of lock cylinders 19 which are connected to the guide shoes 17 and 17' and to the locking plate 16 so that the teeth 2' of the locking plate 16 may engage with or disengage from the teeth of the rack 2 when the lock cylinders 19 are actuated, and a rocking lever 12 whose upper end is pivoted to the upper box 24 with a pin 13 extending through the elongated slot 25 of the plates 18 and the locking plate 16 and whose lower end is pivoted to a clevis securely fixed to the upper surface of the platform 26 with a pin 14, a pair of L-shaped lock plates hinged to the upper end of the rocking lever 12, anda pair of lock cylinders 21 loaded with a spring and connected to the lock plates 20 and the rocking lever 12 so that the lock plates 20 engage with the guides 3. Four platform-supporting-and-locking devices with the construction described above are used to support and lock the platform 26 in position.

Next the mode of operation of lifting or lowering .the platform 26 will be described. The first pair of lift devices or mechanisms are locked in position by the lock cylinders 5. That is, the teeth 2 of the lock plates 6 are engaged with the rack 2, and the rods or plungers of the lift cylinders 4 are extended to the full extent. On the other hand, the lock plates 6 of the other pair of lift devices are disengaged from the rack 2 and the rods or plungers of the lift cylinders 4 are retracted completely. The lock plates 16 of the upper locking devices are disengaged from the rack 2 by the lock cylinders 19. To lift the platform 26, the lock cylinders 5 of the other pair of lift devices are actuated to cause the lock plates 6 to engage with the rack 2, whereas the lock cylinders 5 of the one pair of lift devices are actuated to disengage the lock plates 6 from the rack 2. As a result the platform and the load applied thereto are now supported by the other pair of lift devices. It should be noted that the lock cylinders 5 of the one pair of lift As the plungers of the lift cylinders 4 of the other pair of lift devices are extended, the platform 26 is lifted and the plungers of the lift cylinders 4 of the one pair of lift devices are rapidly retracted. It should be noted that the speed of the retracting plungers is faster than that of the extending plungers. When the plungers of the lift cylinders are fully extended, a limit switch (not shown) is actuated so that the lock cylinders in the one pair of lift devices are actuated to cause the lock plates 6 to engage with the rack 2, whereas the lock cylinders in the other pair of lift devices are actuated to cause the lock plates to disengage from the rack. Thus, one cycle of lifting operation is accomplished. It is seen that the platform 26 may be continuously lifted to a desired height when the above lifting operations are cy cled.

To lower the platform 26, the one pair of lift devices with the lift cylinders extended as shown in FIG. 1 are supporting the platform 26 and the load applied to it so that the lift cylinders are retracted to lower the platform 26 while the lock plates in engagement with the rack 2 support the platform 26 and the load applied to it. In this case, the lift cylinders 4 of the other pair of lift devices are rapidly extended as the no load is applied to them, and actuate a limit switch (not shown) thereby actuating the lock cylinders 5 to engage the lock plates 6 with the rack 2. Thus one cycle of platform lowering operation which is the reverse operation of the lifting operation described above, is accomplished.

While the platform 26 is lifted or lowered in the manner described above, the four platform supportingand-locking devices are so actuated as to disengagethe lock plates 16 and 20 from the rack 2 and the guides 3 by the locking cylinders 19 and 21. Therefore the lifting or lowering operation by the lift devices below the platform will not be interrupted.

When it is desired to lock the platform 26 at a desired position, the four upper locking devices are used. That is, the lock cylinders 19 are actuated to engage the lock plates 16 with the rack 2, and thereafter the hydraulic pressure is relieved from the lock cylinders 21 so that the plungers of the lock cylinders 21 are extended under the force of the springs (not shown) to engage the locking plates 20 with the guides 3 as shown in FIG. 2-E. The locking plates 20 have been in engagement with the guides 3 as shown in FIG. 2-D when the lift devices below the platform '26 were actuated. Thus, even when no hydraulic pressure is applied to the lock cylinders 19, the lock plates 20 are in mechanical engagement with the guides 3 under the force of the springs, whereby the platform 26 may be securely locked in position.

In the instant embodiment, the four lift devices or mechanisms are shown as being actuated to lift or lower the platform. However, when the platform and the load applied to it are too heavy to support only by one pair of the four lift devices, the four lift devices may be simultaneously 'so actuated as to support the platform and the load applied to it. In this case, the supporting-and-locking devices above the platform and the lift devices below the platform are alternately actuated to have their locking plates alternately engaged with the rack and the guides and disengaged therefrom.

In the instant embodiment, the platform has been described as being lifted or lowered with respect to the cylindrical vertical column by the four lift devices disposed below the platform and the four locking devices disposed above the platform, but it will be understood that any number of lift and locking devices may be used depending upon the weight of the platform and the load applied thereto and that the platform may be lifted or lowered with respect to the cylindrical vertical column.

What is claimed is:

l. A lift apparatus comprising a post; a platform fitted over said post for slidable vertical movement; a plurality of racks each of which has trapezoidal teeth and a pair of guides extended on both sides of said rack in the longitudinal direction thereof, and which is attached to the outer surface of said post in the axial direction thereof; a plurality of lift devices disposed below-said platform for lifting or lowering said plat plurality of trapezoidal teeth adapted for engagement I with said trapezoidal teeth of said rack and which isslidably fitted into said box, a pair of lock cylinders operatively coupled to said box and said lock plate so as to cause said lock plate to engage with or disengage from said rack, and a plurality of lift cylinders operatively coupled to said platform and to said lock plate in said box; and a plurality of locking devices disposed above said platform for supporting and locking in posi tion said platform, each of said plurality of locking devices comprising a box formed with a pair of guide shoes slidably fitted over said guides of said rack respectively, a lock plate which has a plurality of trapezoidal teeth adapted for engagement with said trapezoidal teeth of said rack and which is slidably fitted into said box, a pair of lock cylinders operatively coupled to said box and said lock plate so as to cause said lock plate to engage with or disengage from said rack, and a rocking lever interconnecting said lock plate in said box with the top surface of said platform.

2. A lift apparatus as set forth in claim 1 wherein the locking cylinders in said plurality of locking devices disposed above said platform and in said plurality of lift devices disposed below said platform are alternately actuated to lift or lower said platform. 

1. A lift apparatus comprising a post; a platform fitted over said post for slidable vertical movement; a plurality of racks each of which has trapezoidal teeth and a pair of guides extended on both sides of said rack in the longitudinal direction thereof, and which is attached to the outer surface of said post in the axial direction thereof; a plurality of lift devices disposed below said platform for lifting or lowering said platform, each of said plurality of lift devices comprising a box formed with a pair of guide shoes slidably fitted over said guides respectively, a lock plate which has a plurality of trapezoidal teeth adapted for engagement with said trapezoidal teeth of said rack and which is slidably fitted into said box, a pair of lock cylinders operatively coupled to said box and said lock plate so as to cause said lock plate to engage with or disengage from said rack, and a plurality of lift cylinders operatively coupled to said platform and to said locK plate in said box; and a plurality of locking devices disposed above said platform for supporting and locking in position said platform, each of said plurality of locking devices comprising a box formed with a pair of guide shoes slidably fitted over said guides of said rack respectively, a lock plate which has a plurality of trapezoidal teeth adapted for engagement with said trapezoidal teeth of said rack and which is slidably fitted into said box, a pair of lock cylinders operatively coupled to said box and said lock plate so as to cause said lock plate to engage with or disengage from said rack, and a rocking lever interconnecting said lock plate in said box with the top surface of said platform.
 2. A lift apparatus as set forth in claim 1 wherein the locking cylinders in said plurality of locking devices disposed above said platform and in said plurality of lift devices disposed below said platform are alternately actuated to lift or lower said platform. 